Book wrapping with a 36 cm thread:\nA 36 cm thread is used to wrap a rectangular book—lengthwise twice and breadthwise once (tight, no slack). Assuming a square book to make the result unique, determine the book’s area in square centimetres.

Difficulty: Medium

Correct Answer: 144 sq.cm

Explanation:


Introduction / Context:
The thread length equals 2L + B for a rectangle wrapped lengthwise twice and breadthwise once. As stated, many (L, B) pairs satisfy 2L + B = 36, giving different areas. Under the Recovery-First Policy, to render the question solvable and standard, we assume a square book (L = B), which is a common benchmark interpretation for such wrap problems.



Given Data / Assumptions:

  • Total thread = 36 cm.
  • Wraps: twice along length, once along breadth ⇒ 2L + B = 36.
  • Assumption: L = B (square book).


Concept / Approach:
Substitute L = B into the linear relation to get a unique side, then compute area.



Step-by-Step Solution:

1) With L = B = s, 2s + s = 36 ⇒ 3s = 36.2) s = 12 cm.3) Area = s^2 = 12^2 = 144 sq cm.


Verification / Alternative check:
If not assumed square, infinite pairs exist (e.g., L = 9, B = 18), yielding differing areas; hence the square assumption is the minimal fix to make the problem determinate.


Why Other Options Are Wrong:
Other values do not arise from a square satisfying the given wrap relation.


Common Pitfalls:
Using perimeter 2(L+B) instead of 2L + B for the described wrapping; mixing units or ignoring that the statement alone is underdetermined.


Final Answer:
144 sq.cm.

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